The electromagnetic radio spectrum is a significant natural resource. In wireless communications, the transmitter modulates an analog/digital signal according to an allotted portion of the radio spectrum, so as to reach the receiver that can be listening to the signal on the same frequency band. Therefore, in order to control the mutual interference among uncoordinated wireless nodes, i.e. transmitters and receivers, the radio spectrum has traditionally been, and usually is, licensed by governments. However, in practice, such legacy command and control regulations introduce inefficiency into the spectrum resource allocation and its operation. Particularly, some licensed frequency bands are almost never used, or only partially used, whereas remaining frequency bands are heavily occupied. This results in a scarcity of radio spectrum resources for supporting the emerging commercial and/or scientific applications of wireless communications and networking, or fulfilling the demand for existing commercial and/or scientific applications.
For example, according to a recent measurement study of the United States Federal Communications Commission Spectrum Policy Task Force (Federal Communications Commission, “Spectrum Policy Task Force,” Rep. ET Docket no. 02-135, November 2002.), the regulator's static spectrum allocation strategy has resulted in an inefficiency such that the temporal and geographical variations in the utilization of the assigned spectrum range from 15% to 85%. These observations, coupled with the service providers desire to reduce infrastructure costs, have led to the development and promotion of “cognitive radio”. By definition, a cognitive radio can intelligently adjust the wireless communication parameters, in accordance with the ambient radio environment, such that the initiated wireless transmissions will not be interfering with other co-located radio spectrum usage. Further, the cognitive radio will dynamically adjust to the local radio environment, selecting and utilizing a channel based upon availability rather than a predetermined allocation. Therefore, instead of the legacy static spectrum allocation, regulators around the world are now encouraging the new paradigm of dynamic or opportunistic allocation, which can make much more efficient use of the radio spectrum resource and existing infrastructure.
Therefore, when the aforementioned “wireless communication parameters” are of a group of wireless data channels, the cognitive radio paradigm is specified to be “opportunistic wireless channel access”. For one wireless node, it is further defined as the following: the wireless node can opportunistically access one wireless channel, selected from a group of predetermined channels, such that the selected one will not be interfering with other on-going wireless communications. By accessing the aforementioned wireless channel, the wireless node can opportunistically poll one or more other wireless nodes to the selected channel, so as to implement certain types of abstract wireless link communications.
In above, the “predetermined wireless channels” are usually differentiated by distinctive frequencies. It can also be differentiated by other means, such as spreading or autocorrelation signatures, as long as those distinctive channels are orthogonal to (i.e. not interfering with) each other. The “certain types of abstract wireless link” can be any functional abstractions of wireless links, such as broadcast, unicast, multicast/any-cast, or data aggregation, which can necessitate the mutual cooperation among a group of wireless nodes in proximity. A more detailed specification of the wireless link abstractions can be found in the work of Liang Song and Dimitrios Hatzinakos (see for example “Embedded Wireless Interconnect for Sensor Networks: Concept and Example,” in Proc. IEEE Consumer Communications and Networking Conference, Las Vegas, Jan. 10-12, 2007, and “Cognitive Networks: Standardizing the Large Scale Wireless Systems,” in Proc. IEEE 2nd Workshop on Cognitive Radio Networks, Las Vegas Nev., January 2008).
In principle, the operation of a cognitive radio, for opportunistic wireless channel access, is therefore composed of two steps. The first step is “sensing”, where the first node determines one favored channel by evaluating the ambient radio spectrum environment; and the second step is “polling”, where the first node polls a set of second wireless nodes in proximity to the identified channel. Both steps can follow an opportunistic criterion, where the favored channel and the set of second wireless nodes are determined opportunistically, i.e. based on the channel and the nodes availability.
It would be advantageous to provide a method and apparatus for cognitive radio that is able to quickly and effectively implement the aforementioned two steps of “sensing” and “polling”. It would be further beneficial for the cognitive radio method to be compatible with existing wireless standards allowing the benefits to be leveraged in existing infrastructure deployments to provide enhanced utilization and improved quality of service. It would also be beneficial for the method of cognitive radio to operate with multiple wireless standards as commercial electronic devices increasingly support operation according to two or more wireless standards, for example laptop computers sold with integrated WiFi (IEEE 802.11) and Bluetooth (IEEE 802.15.1) transceivers. Additionally, the method should allow the formation, evolution and continued rearrangement of wireless networks.